Underway Replenishment is the method by which supplies are transferred from one ship to another at sea to enable a ship to remain at sea for prolonged periods of time. One current method of underway replenishment involves rigging a cable between the supply ship and the receiving ship and sending supplies over a wire using a trolley system.
An ideal scenario for transfer would be what is referred to as “skin-to-skin” replenishment, which is conducted by transferring material from two ships located directly next to each other. Currently this is possible only when the involved ships are at anchor or are moving at slow speeds in calm seas, due to the forces of water acting between the vessels, and the danger of the vessels colliding even while not making way. This method would be ideal for transfers at higher sea states because it would allow the transfer of supplies in 20 foot containers using standard crane systems. While skin-to-skin replenishment is not possible under all conditions and with all situations, increased capabilities for situations with higher sea states are desired.
One alternative is to develop a crane system that is capable of compensating for the relative movement between ships. However, such systems are highly complex and still may not be safe for transferring containers at higher sea states.
Alternatively, if the supplying and receiving ships can be rigidly attached, materials can be transferred from one ship to the other much more efficiently than previous systems, since complex crane systems would not be required. Larger, heavier loads could be transferred at relatively higher rates from hull to hull if a “catamaran” configuration were achieved between the ships. Further, it is expected that material transfers could be made at sea states of up to 4 or higher.
Accordingly, there is a need for a device which can securely and safely connect two large cargo ships at sea, in conditions of up to sea state 4 or higher, so that transfer of standard 20-foot containers ship-to-ship by crane can be performed.